1. Field of the Invention
The present invention relates to a capacitor with excellent high-frequency characteristics, in which a couple of electrodes having a dielectric between them are made of a metal material, and more particularly relates to a structure of a capacitor suitable for mounting in an integrated circuit and a process for manufacturing this capacitor.
2. Description of Related Arts
As one of prior arts for speeding up the operation of an integrated circuit, which uses a unipolar transistor, such as a MOS transistor, or a bipolar transistor, the so-called copper wiring technology is well known which uses copper with lower electric resistance than aluminum to build circuit wiring previously formed by aluminum.
Regarding the capacitor used in an integrated circuit, it is known that a MIM (Metal-Insulator-Metal) capacitor is superior in high-frequency characteristics and more advantageous for improving the high-speed operation properties of the circuit than the so-called PIP (Polysilicon-Insulator-Polysilicon) capacitor in which a couple of electrodes having a dielectric between them are made of a conductive polysilicon.
It is also well known that it becomes possible to further improve the high-frequency characteristics of the integrated circuit by combining the above-mentioned copper wiring technology and technology for forming the electrodes of the MIM capacitor not by aluminum but by a copper metal material with lower electric resistance than aluminum.
However, the use of copper for the electrodes of the MIM capacitor as mentioned above gives rise to a phenomenon that part of the copper atoms constituting the electrodes diffuse into the dielectric made of silicon oxide, for example, between the electrodes of the capacitor. The diffusion of copper atoms into the dielectric deteriorates the insulation characteristics of the dielectric, and therefore decreases the dielectric property and the durability of the capacitor.
Furthermore, in shaping of the copper electrodes, it has been impossible to apply etching technology, which is used on the aluminum electrode, and therefore it has been difficult to form the copper electrodes in desired shape.